Our long-term goals center on defining the signaling events which coordinate the activity of endothelial cells (EC) and smooth muscle cells (SMC) in microvessels that control the delivery of oxygen and nutrients in accord with tissue metabolic demand. Our working hypothesis is that the local control of blood flow reflects the coordination of activity among EC and SMC of the feed arteries (FA) and arterioles which comprise microvascular resistance networks. Stimulating with acetylcholine (ACh) initiates complementary signals that propagate along the endothelium to relax consecutive SMC along vessel branches: (1) Hyperpolarization via activation of Ca2+-sensitive K+ channels (KCa), referred to as `rapid-conducted vasodilation' (RCVD; velocity > several mm/s) and mediated by electromechanical coupling, whereby intracellular Ca2+ ([Ca2+]i) and SMC (`myogenic') tone change with membrane potential (Vm); (2) A Ca2+ wave that releases nitric oxide, referred to as `slow-conducted conducted vasodilation' (SCVD; velocity, ~110 5m/s) and mediated through pharmacomechanical coupling (i.e., Ca2+ sensitization), whereby SMC tone changes independent of [Ca2+]i. This project is focused on understanding how SCVD is initiated, propagated and interacts with RCVD to control tissue blood flow. Experiments are performed using an established model of hamster FA with Ca2+ indicators in vitro complemented by in vivo studies using transgenic mice expressing a Ca2+ indicator protein (GCaMP2) in arteriolar EC. The source(s) of Ca2+ underlying endothelial Ca2+ waves is unknown. Aim 1 will determine whether release of Ca2+ from internal stores is integral to SCVD by stimulating ryanodine and inositol 1,4,5- trisphosphate (IP3) receptors before and after store depletion. To test whether extracellular Ca2+ ([Ca2+]o) is integral to Ca2+ waves, [Ca2+]o is manipulated along with its entry into EC. In the absence of myogenic tone, Ca2+ waves travel < 300 5m but propagate for ~1 mm when tone is present. Aim 2 will determine why myogenic tone is required for effective propagation of EC Ca2+ waves by manipulating transmural pressure and SMC activation. We will evaluate whether (and if so, how) SMC tone affects EC [Ca2+]i and whether a threshold level of [Ca2+]i is required for EC to propagate Ca2+ waves. When hyperpolarization and RCVD are inhibited by KCa antagonists, the velocity of Ca2+ waves slows to ~20 5m/s. Aim 3 will determine how RCVD interacts with SCVD by evaluating how changing Vm (with transmural pressure, adrenergic agonists, or by manipulating [K+]o) affects the propagation of Ca2+ waves along EC. Further, whereas KCa are activated at the site of ACh stimulation, we will explore why Ca2+ waves do not activate KCa at remote sites. Resolving the nature of Ca2+ waves and the interaction(s) between RCVD and SCVD will provide critical new insight for considering how respective signaling pathways may be affected during such pathophysiological conditions as diabetes, hypertension, and ischemia. We intend for this knowledge to facilitate the development of novel strategies for treating vascular disease and promoting the delivery of oxygen and nutrients to tissues throughout the body.